As frequent travelers know, flight delays are all too familiar. Lately, NASA has been looking into a much less frequent, but a potentially very dangerous problem that has recently caused major disruptions in aviation services … volcanic eruptions.
Explosive volcanic eruptions produce ash, or tiny, hard, jagged particles that can be blown thousands of miles away from their source. Volcanic ash is quite dangerous to airplanes, grounding and diverting flights with a huge economic impact to travelers and citizens who rely on goods and services delivered by aircraft.
In a recent study, researchers are using NASA 3D satellite data to improve forecasts of volcanic ash plumes to benefit aviation.
Currently, NASA has a number of instruments in space that can "see" volcanic ash particles. Each of these instruments provides information about the ash, helping detect, locate and characterize the physical and chemical properties of the ash plume. However, none of these instruments paints a complete enough picture of the ash plume and its constituents to effectively inform the aviation community of the threat. That’s changing.
The eruption of Eyjafjallajokull, a volcano in Iceland, produced a large plume over the airspace of Europe, grounding more than a hundred thousand travelers in 2010 with an impact of more than a billion dollars. This eruption was a wakeup call to the atmospheric science and aviation communities.
"The Icelandic eruption, such a dramatic event, made us take a hard look at what each of our satellites can tell us," said John Murray, associate program manager for the NASA Applied Sciences Program's natural disasters focus area. "We knew we needed to understand how to integrate them to make better forecasts."
Murray knew they needed to look more closely at the unique capabilities of NASA satellite imagery to improve warnings produced by the world’s nine operational Volcanic Ash Advisory Centers (VAACs). These advisory centers use relatively simple representations of atmospheric particles to develop forecasts that are then used to guide decision makers as to where aircraft could safely fly. Such models often provide useful information about the volcanic ash distribution in the short term, but lack accurate information about ash plume concentration, layering, and long-term dispersion.
"The dispersion of a volcanic plume in the atmosphere is like ink in water," explained Jean-Paul Vernier, a researcher at NASA's Langley Research Center. "Models, which are used to simulate both, rely on source information like how much ink or ash is introduced and how the flow –either the current or wind– transports the material."
For longer lasting plumes typically injected at higher altitudes near commercial cruise levels, explained Vernier, forecasters need a combination of trajectory models with refresh information about the plume's height and location. That's where NASA's 3D data comes in.
NASA's CALIPSO satellite mission is uniquely suited to provide updated information about ash plume height and location. CALIPSO, or Cloud Aerosol–Lidar and Infrared Pathfinder Satellite Observations, has used a space-based lidar system to provide an unprecedented 3D view of atmospheric particles, like volcanic ash, and cloud in the atmosphere since 2006.
In their study, the research team focused on the June 2011 volcanic eruption of Puyehue-Cordón Caulle in Chile, which disrupted air traffic throughout much of the Southern Hemisphere. This Chilean eruption was powerful, ejecting ash in the upper troposphere, or 3 to 9 miles above the Earth. The higher ejection caused the plume to be long-lasting, circling the globe at least three full times in the southern latitudes.
CALIPSO data allowed the research team to track the plume on its trip around the globe. Researchers looked at the different channels of the CALIPSO lidar to be able to differentiate between clouds and ash.
"CALIPSO gives us very accurate information about the 3D location of ash," said Vernier. "However, the CALIPSO lidar data comes to us in curtains and we don't know what's between two curtains. We use trajectory models to fill in those gaps."
The team used volcanic ash observations from CALIPSO overpasses as initiation points for the trajectory model. By accumulating several days of observations transported by the model forward in time, it’s then possible to produce a more accurate forecast than using a simple dispersion model.
Duncan Fairlie, research scientist at NASA's Langley Research Center, added that a key advancement with this technique was being able to use "cloud clearing" algorithms, or mathematical formulas, developed by Vernier. These algorithms give a clearer view of the ash and help to distinguish between the ash plume and clouds.
Upon comparing the model results with independent CALIPSO observations, the research team saw that the model successfully reproduced the 3D structure of volcanic ash clouds.
"We saw remarkable agreement between the trajectory model and the independent CALIPSO observations," said Fairlie. "To be honest, we were blown away."
Their results were especially compelling for the aviation community in southern Australia and New Zealand. In the three weeks following the Chilean eruption, the Darwin, Australia VAAC found the Puyehue-Cordón Caulle plume had persisted, however the long-term dispersion model forecast of the plume became increasingly unreliable. Thus, the Darwin VAAC was heavily dependent on fundamental satellite observations, which can't always see through the clouds to locate ash plumes.
"Our model, however, provided additional information about the 3D structure of the volcanic plume, especially the extension of the plume’s forward trajectory that was not available to the Darwin VAAC at the time of their advisories," said Murray. "For example, the model clearly showed the head of the volcanic ash cloud crossing the southern part of Australia directly east of the Darwin VAAC’s advisory area on June 21."
Vernier, Fairlie, Murray and their colleagues are now working with the international volcanic ash community to aid in the integration of CALIPSO data trajectory modeling to the VAAC modeling process to help the aviation community’s efforts to operate more safely and efficiently when volcanic ash events occur. This process is especially challenging with low ash concentrations, such as those observed in this study, because much of the VAAC workload consists of making judgment calls between potential ash and false alarms.
"The combination of CALIPSO observations of volcanic ash clouds and a Lagrangian trajectory model offers a potential new capability that VAACs could use to improve aviation safety worldwide," said Murray.
"Additionally," said Vernier, "future NASA missions, such as SAGE III on ISS, will be useful to continue monitoring the dispersion of volcanic ash in the atmosphere."
Details of this study can be found in the September issue of the American Meteorological Society's Journal of Applied Meteorology and Climatology.
NASA's Langley Research Center